PROPERTY, EQUIPMENT AND SOFTWARE, NET - Schedule of Property, Equipment and Software, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Total property, equipment and software, gross	$ 416,334	$ 436,384
Less: accumulated depreciation and amortization	(331,050)	(311,434)
Property, equipment and software, net	85,284	124,950
Net carrying amount of internally-developed software	57,900	71,100
Warehouse equipment
Property, Plant and Equipment [Line Items]
Property, equipment and software, gross	0	5,144
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property, equipment and software, gross	5,005	9,113
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property, equipment and software, gross	24,808	47,927
Office equipment
Property, Plant and Equipment [Line Items]
Property, equipment and software, gross	676	1,735
Purchased software
Property, Plant and Equipment [Line Items]
Property, equipment and software, gross	435	7,207
Computer hardware
Property, Plant and Equipment [Line Items]
Property, equipment and software, gross	121,307	143,118
Internally-developed software
Property, Plant and Equipment [Line Items]
Property, equipment and software, gross	$ 264,103	$ 222,140

The carrying amount of capitalized computer software costs net of accumulated amortization as of the balance sheet date.

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